Method and composition for electroplating zinc

ABSTRACT

AN AQUEOUS BATH FOR PRODUCING DUCTILE, ADHERENT ZINC ELECTRODEPOSITS UPON METALLIC SURFACES CONTAINS AMMONIUM CHLORIDE, ZINC CHLORIDE AND A SURFACE ACTIVE AGENTS INPONENT COMPRISING A MIXTURE OF SURFACE ACTIVE AGENTS INCLUDING A PRIMARY SURFACE-ACTIVE AGENT SELECTED FROM THE GROUP CONSISTING OF SULFATED POLYOXYALKYL CARBINAMINES, CONDENSATE OF ALKYL PHENOLS AND AN ALKYLENE OXIDE, IMIDAZOLINE DERIVATIVES, AND MIXTURES THEREOF. IN ADDITION, A SECONDARY SURFACE-ACTIVE AGENT IS DESIRABLY INCLUDED SUCH AS PHOSPHORIC ACID ESTERS OF POLYALKYLENE GLYCOLS AND ALKOXYLATED ALKYL PHENOLS AND THE ALKALI METAL SALTS OF SUCH ESTERS, POLYOXYALKYL CARBINAMINES, NATURAL PHOSPHATIDES AND MIXTURES THEREOF. THE BATH HAS A PH OF 3.0 TO 10.0 AND MAY ADDITIONALLY CONTAIN ALDEHYDE BRIGHTENERS, BUFFERING AND CHELATING AGENTS, AND SECONDARY BRIGHTENERS.

United States Patent US. Cl. 20455 R 33 Claims ABSTRACT OF THE DISCLOSURE An aqueous bath for producing ductile, adherent zinc electrodeposits upon metallic surfaces contains ammonium chloride, zinc chloride and a surface active component comprising a mixture of surface active agents including a primary surface-active agent selected from the group consisting of sulfated polyoxyalkyl carbinamines, condensate of alkyl phenols and an alkylene oxide, imidazoline derivatives, and mixtures thereof. In addition, a secondary surface-active agent is desirably included such as phosphoric acid esters of polyalkylene glycols and alkoxylated alkyl phenols and the alkali metal salts of such esters, polyoxyalkyl carbinamines, natural phosphatides and mixtures thereof. The bath has a pH of 3.0 to 10.0 and may additionally contain aldehyde brighteners, buffering and chelating agents, and secondary brighteners.

REFERENCE TO RELATED APPLICATIONS This application is a continuation-in-part of our copending application Ser. No. 711,504, filed Mar. 8, 1968, now abandoned, entitled Method and Composition for Electroplating Zinc, which was in turn a continuation-inpart of our application Ser. No. 626,951, filed Mar. 30, 1967, and entitled Composition and Bath for Electroplating Zinc, now abandoned.

BACKGROUND OF THE INVENTION Various baths have been utilized for electroplating zinc onto metallic substrates and such baths have been widely employed. The most common baths are those utilizing sulfates and cyanides as the electrolytes, although it has been suggested that other salts may be utilized or included therewith such as chlorides.

Generally, the cyanide baths have proven highly effective despite certain objectionable features such as toxicity, difficulty in disposal, low current efficiency, embrittlement of certain steels and the difiiculty in effecting deposition on cast and malleable irons. The sulfate baths overcome many of the objections to the cyanide baths, but exhibit low throwing power, poor efiiciency at low current densities and secondary anode corrosion with metal increase in the bath. In addition, the sulfate baths tend to produce dull zinc deposits.

It is an object of the present invention to provide a novel chloride plating bath for producing adherent ductile zinc deposits.

It is also an object to provide such a bath which is operable over a Wide range of current density and with high current efficiency While affording excellent throwing power and operability at low voltage.

Another object is to provide such a bath which is effective in depositing zinc upon cast and malleable irons and which may produce bright deposits over a wide range of operating conditions.

A further object is to provide a method for electroplating zinc utilizing such an improved chloride plating bath so as to obtain highly advantageous adherent and ductile zinc deposits at relatively low cost.

SUMMARY OF THE INVENTION It has now been found that the foregoing and related objects can be readily attained by use of an aqueous bath containing 10-250 grams per liter of ammonium chloride, 20-220 grams per liter of Zinc chloride and (HS-45.0 grams per liter of a surface-active component comprising a mixture of surface active agents including a primary agent selected from the group consisting of sulfated polyoxyalkyl carbinamines, imidazoline derivatives, condensates of an alkyl phenol having an alkyl chain of 6-12 carbon atoms with an alkylene oxide selected from the group consisting of ethylene oxide and propylene oxide, and mixtures thereof. The bath is operable at a pH of 3.0 to 10.0 and at current densities of from less than 1.5 to more than 400 amperes per square foot.

The term zinc chloride is used for convenience since the bath is a chloride bath. However, the zinc may be added as some other soluble zine compound which does not introduce an interfering ion. In particular, zinc oxide has been found useful because of its availability in a relatively high purity. The soluble zinc in the bath is thus calculated as zinc chloride.

The system desirably includes a secondary surface active agent selected from the group consisting of phosphoric acid esters of polyalkylene glycols or alkoxylated alkyl phenols and the alkali metal salts of such phosphate esters, polyoxyalkyl carbinamines, natural phosphatides, alkyl amido betaines, the alkali metal salts of N-tallow beta-amino propionate, partial alkali metal salts of N- lauryl-beta-iminopropionate and mixtures thereof.

In addition to the foregoing essential components, the bath may contain about 0.04 to 0.40 gram per liter of various primary brighteners, small concentrations of secondary brighteners, buffering agents, chelating agents and other components which have a tendency to increase the throwing power of the bath at low current densities, all of which will be discussed in detail hereinafter.

Exemplary of preferred baths are the following compositions:

BATH N0. 1

Range of Make-up operation (grams/ (grams! Compound liter) liter) Anhydrous zinc chloride 70 6595 Ammonium chloride 100 90-120 65 50-70 N onyl phenoxy polyethoxy ethanol (11 mols ethylene oxidefl mol nonyl phenol) 0. 1 0. 02-0. 3

2-capryl-1-(ethyl-beta-oxypropanoic aeid)-imidazoline 0. 1 0. 04-0. 4 Ortho-chlorobenzaldehyde 0. 1 0. 04-0. 5

The above bath may be operated in a pH range of 6.9-7.5, and preferably at about 7.2, and at a prefered temperature range of about 95 Fahrenheit.

The above bath may be operated in a pH range of 6.2- 7 .5 and preferably about 6.9-7.3. The preferred tempera. ture of operation is about 80-95 Fahrenheit.

The primary surface active agent As indicated previously, condensates of alkyl phenols and alkylene oxides have been found to be one of the three classes of surface-active components operable to provide the desired action to the baths of the present invention. Generally, the alkylene oxide will be present in a molar ratio of the alkyl phenol of about 8 to 25:1 and is either ethylene oxide or propylene oxide. The alkyl substituent on the phenol has a carbon chain of 6-12 carbon atoms and preferably 8-10.

Exemplary of such condensates are octyl phenoxy polyethoxy ethanols and nonyl phenoxy polyethoxy ethanols with the preferred agents being nonyl phenoxy polyethoxy ethanols having a molar ratio of about 10 to 20:1.

The alkylene oxide-alkyl phenol condensate is used in a concentration of 0.345 grams per liter and preferably about 1.0-7.5 grams per liter depending upon the remaining components of the bath, the pH, and the presence of other surface active agents in combination therewith.

The second class of surface-active agents operable for the primary component are the amphoteric sulfated polyoxyalkyl carbinamines which evidence stability for extended periods of time under the plating conditions. Generally, these carbinamines are produced by sulfating the terminal hydroxyl group on the polyoxyalkyl chain and may be an alkali metal salt. The etficacy of a particular member of this family should be tested in a laboratory bath since the remaining elements of the bath and the intended conditions of operation tend to limit the breadth of application. However, it has been found that essentially universal suitability is provided by the sulfated polyoxyalkyl tert.-carbinamines having the general formula:

in which R R and R are alkyl groups having a total of 7-23, and preferably eleven to fourteen, carbon atoms wherein in has a value of from 8-25, and preferably 12.5 to 17.5, and X is a monovalent cation selected from the class consisting of hydrogen and alkali metals. Surfaceactive agents of this type are described in detail in U.S. Pat. No. 3,079,416, granted to Rohm & Haas Company on Feb. 26, 1963, as the assignee of Jean Dupre et al.

The third class of surface-active agents operable for the primary component are the imidazoline derivatives corresponding to the fol-lowing general formula:

In the foregoing formula, R represents an alkyl radical having to 24 carbon atoms; G is OH ion, an acid salt radical, an anionic surface-active sulfate salt radical such as preferably OSO OR, or an anionic surface-active sulfonate salt radical; and Z is COOM, CH COOM, or HO-CH--CH SO M radical. The substituent designated M in the foregoing formula is a hydrogen atom, an alkali metal or an organic base, and that designated Y is either an --OR' or --N(R') A group. Each R substituent is independently selected from the group consisting of hydrogen, alkali metals, and CH COOM; A represents an anionic monovalent radical and n represents an integer from 1 to 4. Use of the dotted line representation for the bonds connecting the substituents G and CH Z to the nitrogen atom indicates that these substituents are optionally present or absent, but it should be understood that they are either both present or both absent. Desirable compounds are provided when, in accordance with the foregoing formula, G represents the radical OSO OR,

particularly in which R is a C to C alkyl group, and Z is a COOM radical in which M is preferably an alkali metal cation.

Exemplary of the compounds corresponding to the time going formula which are satisfactory for use in the baths described herein are Z-alkyl-1-(ethyl-beta-oxypropanoic acid) imidazolines wherein the alkyl group is capryl, undecyl or a mixture of C -C chains, and the disodium salt of lauroyl-cycloimidinium 1 ethoxyethanoic acid 2- ethanoic acid.

As will be readily appreciated, these three classes of compounds may be used in combinations with each other for highly desirable operation. However, even greater benefits are obtained when such an admixture is utilized in conjunction with a secondary surface active agent and with brighteners.

The total amount of the primary surface-active agents may vary from as little as 0.75 gram per liter to as much as 45.0 grams per liter. Generally, this class of constituents will be present in an amount of about 15-200 grams per liter, and, most desirably, about 30-100 grams per liter. The amounts of each in the several mixtures possible which will produce optimum results may readily be determined in a test cell.

The secondary surface active agents Although satisfactory bright to matte deposits may be obtained by use of the alkoxylated alkyl phenol or the sulfated polyoxyalkyl carbinamine as the sole surface active agent, it has been found that the brightness of the deposit and, in some instances, both the brightness and the operable range of current density can be significantly improved by use of a secondary surface active agent in combination therewith. The optimum ratio of the alkoxyl ated alkyl phenol to the secondary surface active agent(s) will vary with the particular components selected, the amounts of the salts and the intended pH and current density for operation.

Secondary surface active agents which have proven highly advantageous are anionic phosphate esters formed by reacting with phosphoric acid alkylene oxide condensates having the general formula:

wherein R is selected from the class consisting of alkoxy compounds having ten to fifteen carbon atoms in the alkyl portion thereof and alkyl phenoxy groups having four to ten carbon atoms in the alkyl portion thereof. The alkoxy units are provided by a value of 5 to 25 for x. Generally, only one hydrogen will be replaced in the esterification reaction, although some minor portion of the reaction product may include esters wherein more than one hydrogen has been removed from the phosphoric acid. In addition to the acid esters produced by the reaction, the unsubstituted hydrogens may be replaced by alkali metals. An extensive description of the anionic phosphate esters is set forth in US. Pat. No. 3,310,496, granted Mar. 21, 1967, to Rohm & Haas Company, as assignee of Richard C. Mansfield et al.

Another group of surface active agents which may be employed are the polyoxyalkyl carbinamines such as are also described in the aforementioned Mansfield et al. Pat. No. 3,310,496. The carbinamines may also be sulfated by reaction with a terminal hydroxy group on the polyoxyalkyl chain. Generally, the preferred carbinamines have the following formula:

wherein R is an alkoxy group having about ten to fifteen carbon atoms in the alkyl portion thereof or an alkyl phenoxy group having four to ten carbon atoms in the alkyl portion thereof. R and R may be hydrogen or relatively short chain alkyl groups providing a total number of carbon atoms of at least one and less than eight.

Still further secondary surface active agents are the 30 to 150 grams per liter of zinc chloride. When it is natural phosphatides or lecithins, alkyl amido betaines, desired to employ lower concentrations of ammonium the disodium salt of N-tallow-beta-amino dipropionate chloride on the order of about 4-5 to 65 grams per liter, and the partial sodium salt of N-lauryl-beta-iminopropithe preferred baths are those containing about 120' to onate. Various other proprietary amphoteric surface active 150 grams per liter of zinc chloride. When it is desired agents have shown useful properties in the systems of the to employ intermediate concentrations of ammonium chlopresent invention. ride on the order of 100165 grams per liter, the preferred Of the several classes of secondary surface active baths are those containing about 60-95 grams per liter of agents, the anionic phosphate esters have proven highly zinc chloride. effective in relatively low concentration although exhibit- To determine the effect of varying the concentration ing a tendency to reduce the efficiency of the bath. For of zinc ammonium and chloride ions, a series of baths baths of higher metal concentration (greater than about was prepared with the pH being adjusted to 8.0 by the 22 grams per liter), the alkyl amido betaines have also addition of ammonium hydroxide. The tests were pershown highly beneficial results. Generally, the other formed in a standard Hull Cell using standard cold rolled classes of secondary surface active agents improve the 1 steel panels. The applied current was 3 amperes and the brightness of the deposit but do not significantly extend baths were maintained at a temperature of about to the useful range of current density. 24 centigrade. The plating time was three minutes. After It will be appreciated that two or more of the secondary platmg, the panels were washed and dried and the panels surface active agents may be used in combination with were examined. In all cases, the deposits were ductile and the P y Surface active agent Paftlclllarly advanta 20 adherent. The analysis of the several baths and the plating geous is an admixture of the anionic phosphate esters with ranges in which the deposit was brought or semi-bright polyoxyalkyl carbinamines. Another combination which are set forth in Table 1 below.

TABLE 1 1 2 3 4 5 6 7 8 9 1 Nrnol, g./l 250 250 250 13.4 25.8 53.5 125 13.4 53. 110 1 20 40 100 68 (is cs 20 136 136 1131304, g./l 20 20 1Q Plating range, amp/ft. 5-120 1.5-120 1.0-120 1.5-120 1.5415 4 ,545 4 4 Polyvinyl alcohol, g./l 75 75 .75 75 75 p-Anisic aldehyde bisulfite, g./l .8 .s .s .8 .s Citric acid, g./l w 4O 40 40 40 40 4.0 Dimethyl sulfoxide, m1./l 75 75 75 75 o-Anisaldehyde, mL/l .25 .25 .25 .Alkylamine polyethoxy sulfate, (QS-15, Rohm dz Haas), Inl./l.... 3. 6 3. 6 3. 6 75 .75 75 3.6 .75 75 Calcium lignosulfonate, g./l 7 17 17 8 8 8 8 8 8 1 t} This bath produces a bright deposit at currents of 10 amperes with current densities of greater than 400 amperes per square foot to provide a broader p a mg range it Bath produced seml bright deposits to 120 amperes per square foot.

3 Semi-bright.

! Bright.

has proven effective is the combination of the imidazolines Qther components with. unsulfaled polyoxyalkyl ternary carbmammes Such Various brighteners may be used in combination with 32 l 9 6 g t l k oh rr?& l l aa s %o in a ii zfs 58 3 22 3? e Surface active agent to improve brightness to the Bemer p y g extent of extreme specular reflectivity including the aryl Generally, the primary and secondary surface active gi iggg zg zi gg figgg l fiz fifg iziy gfi gfi agents may be employed.m a combmed i b of about includes alkaryl aldehydes, and such alkyl and aryl alde- 85 8 i??? fiz g j ig g 25; 1 22: 33i? hydes may be halogenated. Exemplary of such brighteners are o-anisaldehyde, p-anisic aldehyde bisulfite, furfural, f most flame i the.s1.1r.face acme agerlts are glutaraldehyde, veratraldehyde, propionaldehyde, benzalsrrably diluted with water 1mt1ally before adding to t e dehyde o ch1 or obenzal dehy de, and p ch1orobenzal dehy dc, Iemamder of the bath benzylidene, and the aforedescribed imidazoline deriva The zinc and ammonium compounds tlves- The brlghtener is employed 1n a concentration of about G y, the bath y Contaln 20 to 220 grams P 0.04 to 1.50 grams per liter. Above a concentration of liter of zinc chloride but is preferably maintained Within about 0.50 gram per liter there is a decrease in the current t range of about 35 t0 grams P liter- At above density range through which a satisfactory plate can be 150 grams P liter, tbe deposit tends to be Sembbright 10 obtained, and there is also a tendency to decrease the matte y, and below about 35 grams P liter the deposit adherence and ductility of the plated deposit. When nectends to be semi-bright. As previously indicated, the zinc ar th b i ht may b dd d by di l i it i m y be introduced as another Soluble Zinc comboubd a suitable solvent miscible with water such as dimethylsuch as zinc oxide although the amount thereof in the sulfoxide, methanol, ethanol, etc.

bath is calculated as zinc chloride. When the zinc chloride concentration in the bath is The ammonium chloride concentratlon is generally greater than about 100 grams per liter and the ammowithin the range of a out 10 i0 250 grams P and nium chloride concentration is less than 75 grams per is preferabl about 50-150 grams per liter. Below about liter, other substances have been found to exhibit some 50 grams per liter, there is a tendency for the deposit to secondary brightening action, such as polyvinyl alcohols,

be semi-bright to matte grey. The bath also tends to exgelatin, animal glue, evaporated milk, etc. However, the hibit reduced conductivity. For a broad range of current optimum brighteners ar those set forth h einb f density for a bright deposit, the ammonium chloride Buffering agents may be employed if desired to stashould be present in an amount providing a molar ratio bilize the pH of the film formed at the cathode and to to zinc chloride of 1:1 to 20:1. When the molar ratio of 7 maintain the pH value within limits which are optimum ammonium chloride to zinc chloride is less than 1:1, the for obtaining good quality deposits. Exemplary of such deposit tends to be semi-bright to matte grey. buffers are boric acid and acetic acid, and they may be When it is desired to employ a high concentration of added in amounts of about 5 to 30 grams per liter. ammonium chloride on the order of 200 to 250 grams Chelating agents such as citric acid and malic acid are per liter, the preferred baths are those containing about desirably added to prevent the precipitation of basic zinc compounds either in the body of the plating bath or at the surface of the anode and also serve to provide buffering action. Such chelating agents are added in amounts of to 100 grams per liter, and preferably about 45 to 75 grams per liter.

Conditions of operation The baths of the present invention may be operated at ambient temperatures and up to about 70 Centigrade. As the temperature is increased, there is a tendency for the minimum current density for satisfactory plating to increase, and a simultaneous increase in the maximum current density at which satisfactory plating can be obtained. The baths are preferably operated at a temperature of about 20 to 40 centigrade.

The baths of the present invention are effective in a pH range of about 3.0 to about 10.0. However, with a bath containing ammonium chloride in amounts of above about 150 grams per liter at a neutral pH of about 6.7 to 7.0, there is experienced considerable difficulty in preventing the components from salting out even though the amount of citric acid or other chelating agents added is increased. Accordingly, the preferred composition will tend to vary with the intended pH for operation of the bath. From the standpoint of the pH for optimum operation at a range of low to medium high current densities, these baths are preferably operated at a pH of about 6.87.5.

From the standpoint of most efficient operation at low current densities, the baths are preferably operated at a pH of about 6.89.0 and, most desirably, at about 7.0-8.5. When very high current densities are to be employed, the baths are desirably on the acid side. The preferred acid baths have a pH of about 4.5-5.5. Accordingly, when the baths are to be operated at very high current densities, i.e., greater than 200 amperes per square foot, acid baths are preferable; and when the baths are to be operated at relatively low current densities of less than 50 amperes per square foot, slightly alkaline baths are preferable. By use of baths havm 'g a pH of about 6.87.5, operation at a range of current density from low to medium high can be obtained. The pH of the baths may be adjusted by use of citric acid, boric acid, ammonium hydroxide or hydrochloric acid so as to avoid the introduction of possible interfering ions.

Various zinc anodes may be employed including pure zinc and the zinc alloys which are conventionally used in cyanide baths such as zinc aluminum, zinc calcium and zinc magnesium. Corrosion problems at the anode are materially reduced by the baths of the present invention so that pure zinc anodes are highly advantageously employed. Moreover, it has been found that even small amounts of metallic impurities in the anodes such as lead, iron and cadmium can be readily solubilized with resultant inteference in the optimum operation of the bath. Accordingly, highly refined anodes of high purity are most desirably utilized. Insoluble anodes are not desirable because of the possibility of generating nitrogen trichloride which is highly explosive.

The baths of the present invention provide extremely high conductivity and are operable at very low voltages with high plating efficiencies; however, the current efficiency will tend to vary with the particular components selected and their ratio. For example, a Hull Cell operated at 3 amperes requires the use of only about 2.2 volts with the preferred composition. The baths exhibit excellent throwing power over a wide range of current densities so that efficient plating of castings may be effected.

The current densities at which bright deposits are obtained will vary with the particular composition of the bath. Generally, the optimum formulations will provide bright deposits through a range from less than 1.5 amperes per square foot to greater than 400 amperes per square foot. Even with formulations which do not provide a bright deposit of specular reflectivity, adherent bright to dull matte deposits are obtained over a wide range. As

indicated herein, acid baths may be desirable where high speed plating is required whereas the neutral to alkaline baths are preferable where low current densities are to be encountered. Brightness may be effected by the addition of various combinations of brightening agents to the basic formulation as indicated hereinafter.

Agitation is desirable to obtain deposits which are uniform and of high quality and to avoid development of anode sludge and film. Not only is agitation of the bath itself preferable, but agitation of the anode has also been found to be beneficial in reducing any tendency for accumulation of sludge thereat. Agitation of the cathode may be desirable in most instances to obtain a uniform plate and to enable extension of the range of satisfactory current density to higher levels.

The process is adapted to both still plating and barrel plating apparatus with equal efficacy. Filtration of the bath is not essential but will normally be beneficial when contamination of the bath is encountered due to air-borne impurities and carry-over from other finishing operations. Various filtering media may be utilized including fabric, porous stoneware and other conventional filtering materials.

The depletion of the various components of the bath is best corrected by analysis for the several components on a periodic basis which can be established for a given facility. To determine the necessity for the addition of surface active agent, the surface tension of the bath may be measured and quantities of agent added as may be determined by a suitable schedule for the given facility. To determine the amounts of zinc chloride ammonium chloride required, the total chloride ion and the zinc content of a sample are determined and the amount of ammonium chloride is calculated by the difference in chloride ion concentration. The amount of brightener required is best evaluated by testing a sample of the bath in a suitable test cell.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Illustrative of the efficacy of the present invention are the following specific examples wherein all parts are parts by weight unless otherwise indicated.

Example 1 An aqueous bath was prepared containing 40 grams per liter of anhydrous zinc chloride, 250 grams per liter of ammonium chloride, 20 grams per liter boric acid, 3.6 millilites per liter of octyl phenoxy polyethoxy ethanol (16 mols ethylene oxidezl mol octyl phenol), 0.17 gram per liter of calcium lignosulfonate, 0.75 milliliter per liter of dimethyl sulfoxide and 0.25 milliliter per liter of o-anisaldehyde. The pH was 8.2. The bath was a clear bath free from suspended matter.

A panel of low carbon cold rolled steel was utilized in the first test in the standard Hull Cell. The bath was operated at a temperature of 22.2 centigrade. A pure zinc anode was employed and a current of 3 amperes was applied across the cell, developing a potential of 2.2 volts. After three minutes, the panels were removed and rinsed.

Upon inspection of the panels so-placed, it was found that a bright deposit was obtained at current densities of less than 1.5 amperes per square foot to more than 120 amperes per square foot. The deposit showed specular brightness and was free from burning throughout the range of current densities indicated. Subjecting the panels to severe bends about relatively sharp radii did not produce any evidence of cracking of the plated deposits or lack of adherence of the deposit to the substrate. Except at the upper limit of the bright plating range indicated, no gas evolution was observed, indicating essentially percent current efficiency.

Example 2 The procedure of Example 1 was substantially repeated substituting for the octyl phenoxy polyethoxy ethanol of that example the following surface active agents:

(A) Octyl phenoxy polyethoxy ethanol (9.6 mols ethylene xide:1 mol octyl phenol).

(B) Oct yl phenoxy polyethoxy ethanol (20 mols ethylene oxidezl mol octyl phenol).

(C) Octyl phenoxy polyethoxy ethanol (12.5 mols ethylene oxiderl mol octyl phenol).

Upon plating, the test panels from the several solutions were examined and the following results were obtained. Test panels from baths A, B and C were bright over a current density of less than 1.5 to more than 90 amperes per square foot. Excessive burning was observed above the stated range. The deposit was observed to be specular birght and was found to resist cracking and to adhere firmly in a bending test. Gas evolution was observed only in the burning range, indicating substantially 100 percent current efliciency in the plating range.

Example 3 The test procedure of Example 1 was substantially repeated utilizing the octyl phenoxy polyethoxy ethanol in the following amounts: 1.1 milliliters per liter, 1.85 milliliters per liter, 2.63 milliliters per liter, 7.5 milliliters per liter and 37.5 milliliters per liter.

Test panels fom the several baths Were evaluated. The first four baths all produced bright deposits beginning at a current density of somewhat less than 1.5 amperes per square foot, Whereas the highly concentrated bath did not produce a deposit below about 2.5 amperes per square foot. The maximum current density at which a bright deposit was obtained increased from greater than 60 amperes per square foot in the first bath to greater than 75 amperes per square foot in the last two baths. The plate was specular bright in all baths Within the stated current density ranges, and the panels were free from burning throughout the stated ranges. Burning was evident in the panels produced from the first three baths at above the stated maximum current densities for the bright plate. Gas evolution was not observed within the current density range for bright plating. In all instances, the deposits were firmly adherent and resistant to cracking in a bending test.

Example 4 The procedure of Example 1 was repeated except that calcium lignosulfonate was omitted. Upon plating, the minimum current densities at which a satisfactory plate was obtained was found to be about 2.5 amperes per square foot. The deposit was specular bright throughout and free from burning throughout the stated range. Again, the deposit was firmly adherent and resistant to cracking in a bending test.

Example 5 The test procedure of Example 1 was repeated omitting both the calcium lignosulfonate and the o-anisaldehyde and dimethyl sulfoxide. The plate produced by this bath was found to be fine grained but only semi-bright throughout the range of about 2.5 to greater than 120 amperes per square foot. Some gas evolution was observable throughout the entire range. The deposit was found to be free from burning throughout the stated range and was found to be adherent and resistant to cracking in the bending test.

Example 6 The test procedure of Example 1 was repeated omitting the o-anisaldehyde and the calcium lignosulfonate. The plated panels evidenced semi-bright deposits in the range of less than 1.5 to more than 120 amperes per square foot. The deposit was free from burning throughout the stated range and was found to be adherent and resistant to cracking in a bending test.

Example 7 The test procedure of Example 1 was repeated omitting the o-anisaldehyde, the calcium lignosulfonate and the dimethyl sulfoxide. The plated panels evidenced semibright deposits in the range of less than 1.5 to more than 120 amperes per square foot. The deposit was free from burning throughout the stated range and was found to be adherent and resistant to cracking in a bending test.

Example 8 The test procedure of Example 1 was repeated with the substitution for the calcium lignosulfonate, the oanisaldehyde and the dimethyl sulfoxide, of lauroyl cycloimidinium-l-ethoxy ethanoic acid-2-ethanoic acid, sold by Miranol Chemical Company under the designation Miranol CZM. This substance was used in the acid form and in a concentration of 1.4 milliliters per liter. The pH was 8.2.

Upon plating, the specimens were found to have a bright plate in the current density range of less than 1.5 to more than 120 amperes per square foot. The deposit was found to be specular bright and there was no evidence of burning. No gas evolution was observed over the entire surface of the panels. Upon bending, the plate was found to be firmly adherent and free from cracking.

Example 9 The test procedure of Example '1 was repeated substituting for the o-anisaldehyde 1.4 milliliters per liter of a solution containing benzylidene in methanol (10 volume percent). Upon plating, the panels were found to have a specular bright deposit in the current density range of less than 1.5 to greater than 120 amperes per square foot and there was no evidence of burning. No gas evolution was observed over the entire surface of the panels. Upon bending, the plate was found to be firmly adherent and free from cracking.

Example 10 The test procedure of Example 1 was repeated substituting for the o-anisaldehyde and dimethyl sulfoxide 1.0 milliliter per liter of an aqueous solution containing grams per liter of p-anisic aldehyde bisulfite.

The plated specimens were found to have a bright plate throughout the current density range of less than 1.5 to more than amperes per square foot. The deposit was found to be specular bright and there was no evidence of burning. No gas evolution was observed over the entire surface of the panels. Upon bending, the plate Was found to be firmly adherent and free from cracking.

Example ll The test procedure of Example 1 was repeated substituting for the o-anisaldehyde and dimethyl sulfoxide, 1.0 milliliter per liter of a solution of furfural in methanol (25 volume percent).

Upon plating, the specimens were found to have a bright plate in the current density range of less than 1.5 to more than 120 amperes per square foot. The deposit was found to be specular bright and there was no evidence of burning. No gas evolution Was observed over the entire surface of the panels. Upon bending, the plate was found to be firmly adherent and free from cracking.

Example 12 The test procedure of Example 1 was repeated omitting the boric acid. A bright plate was obtained in the range of less than 1.5 to more than 120 amperes per square foot. No burning was observed, and no gas evolution occurred except at the extreme upper end of the plating range. The deposit was found to be firmly adherent and resistant to cracking in the bending test.

Example 13 The bath of Example 1 was utilized in plating standard A2 inch malleable iron pipe elbows. The apparatus employed was a barrel plating apparatus using a commercially pure Zinc anode. The bath was maintained at a temperature of 20 to 24 centigrade. Plating was continued 1 1 for a period of thirty minutes at a current density (based upon the surface area of the parts) of 15 amperes per square foot.

After Washing and drying, the elbows were found to have a bright plate over the entire outside surface and through a distance of about /2 inch from each orifice on the inside surface. A matte grey zinc deposit was observed through the remainder of the inside surface of the casting.

Example 14 The test procedure of Example 13 was repeated substituting for the iron fittings wood screws of a low carbon steel. A bright plate was produced over the entire surface of the screws, including the depths of the threads. The screws were subjected to severe bending, and the deposit was found to be firmly adherent and resistant to cracking.

Example 15 A bath was prepared utilizing the following composition:

G./l. Anhydrous zinc chloride 70 Ammonium chloride 100 Citric acid 65 Sulfated polyoxyalkyl tert-carbinamine (QS15,

Rohm & Haas) 3.4 Nonyl phenoxy polyethoxy ethanol (11 mols ethylene oxide:1 mol nonyl phenol) 0.1 2-capryl -1 (ethyl-betaoxypropanoic acid)-imidazo line 0.1 Ortho-chlorobenzaldehyde 0.1

The bath was heated to a temperature of about 8590 Fahrenheit and had the pH adjusted to about 7.2.

Roller skates of a ferrous metal alloy were supported on a rack and immersed in the bath for a period of about 18 minutes. The current density averaged at about 1520 amperes per square foot.

Upon removal from the bath and rinsing, the roller skates were found to have a zinc deposit of uniform specular brightness.

Example 16 The bath of Example 15 was utilized in a barrel plating apparatus for the plating of screws of a ferrous metal alloy. The temperature of the bath was maintained at about 85-90 Fahrenheit and the screws were plated over a period of about 45 minutes at a current density ranging from about -15 amperes per square foot.

After plating, the screws were rinsed and found to have a uniform bright deposit evidencing specular reflectivity.

Example 17 In order to determine the current efficiency of the bath of Example 1, test panels were plated therein under controlled conditions. The actual weight gain of the panels was measured and compared against the theoretical deposit obtainable from the currents supplied to the plating cell. The actual efiiciency, based upon the theoretical efficiency, was determined to be 86 percent (:5 percent). The test panels were found to have uniform brightness and to have a deposit of specular reflectivity.

' Example 18 A series of baths were prepared using imidazoline derivatives as the primary surface active agent alone and in combination with other primary surface active agents and other components to demonstrate the effects of the several components in combination.

Part A A first bath was prepared by admixing 70 grams per liter zinc chloride and 150 grams per liter ammonium chloride, and then neutralizing the resultant bath to a pH of 7.0 by the addition of ammonium hyroxide. Thereafter, 4 grams per liter of N,N,N-diethylcarboxyl, methylcarboxy-N-[beta-ethyl-1(2 heptyl-2 imidazoly)] am- 12 monium chloride was admixed therewith. In plating in a standard Hull Cell with the bath thus prepared, it was found that a specular bright plate could be obtained over a range of about 1.0- amperes per square foot although there was a yellow caste to the deposit and there was a tendency for salting at the anode.

Part B The procedure of Part A was repeated substituting for the imidazoline derivative thereof, an imdiazoline derivtive corresponding to the general formula set forth hereinbefore wherein Y is -OCH COONa, Z is COONa, G is -OH, and R is C H Similar deposits of highs specular brightness with a yellow caste are obtained on the test panels over the range of 1.0-120 amperes per square foot.

PART C The procedure of Part A is repeated except that there is initially admixed with the zinc and ammonium chlorides 60 grams per liter of citric acid. The tendency for salting is eliminated, and a bright deposit is obtained on the Hull Cell panel throughout the range of 1.0-120 amperes per square foot except in the range of 2.0-'6.0 amperes per square foot where a matte grey adherent deposit is formed.

Part D The procedure of Part C is repeated but there is added with the imidazoline derivative 4.0 grams per liter of an ethylene oxide-nonyl phenol condensate containing 11 moles ethylene oxide per mol of nonyl phenol. The bath thus formed is found to produce deposits which are bright throughout the full range of 1.0 to 120 amperes per square foot although a yellow caste is still apparent. No salting is apparent.

Part E The procedure of Part D is repeated except that there is also added 0.2 gram per liter of ortho-chlorobenzaldehyde. The panels produced by this bath are specular bright without the yellow caste evident with the panels produced by the other baths.

It has also been found that the zinc deposits produced in accordance with the present invention are extremely receptive to chromate treatments so as to obtain a high degree of corrosion protection as Well as an enhancement of the brightness thereof. By use of the preferred neutral to alkaline baths, there has been observed little, if any, evolution, of hydrogen gas at the cathode so that plating of steels susceptible to hydrogen embrittlement is feasible. Even in the acid baths, it is believed that the hydrogen evolution does not tend to produce hydrogen embrittlement.

Thus, it can be seen that the present invention provides a novel and highly effective bath for electroplating zinc on various metallic substraces which is adapted to facile and extremely useful plating of castings because of its excellent throwing power and operability over a wide range of current densities. Since the bath is operable at low voltage, it will produce a high yield per hour at a given current input, particularly because of the high current efliciency. The deposits are adherent and ductile offering significant advantages from the standpoint of wear resistance, and the deposits are also bright, specular and free from burning over relatively wide ranges of current density. Moreover, it can be seen that the chloride baths of the present invention may be readily disposed of so as to significantly reduce the costs of Waste disposal programs.

Having thus described the invention, we claim:

1. An aqueous bath for producing a ductile, adherent zinc electroplated deposit comprising 10 to 250 grams per liter of ammonium chloride, 20 to 220 grams per liter of zinc chloride, and up to 45.0 grams per liter of a surface active component comprising a mixture of surface active agents including at least 0.75 gram per liter of a primary agent selected from the group consisting of sulfated polyoxyalkyl carbinamines, condensates of an alkyl phenol having an alkyl chain of 6-12 carbon atoms with an alkylene oxide selected from the class consisting of ethylene oxide and propylene oxide, imidazoline derivatives, and mixtures thereof, said bath having a pH of 3.010.0, said mixture including one of said primary agents and at least one additional surface active agent selected from the class consisting of another one of said primary agents and secondary surface active agents selected from the group consisting of phosphoric acid esters of polyalkylene glycols and alkoxylated alkyl phenols and the alkali metal salts of such esters, polyoxyallcyl carbinamines, natural phosphatides, alkyl amido betaines, the alkali metal salts of N-tallow-beta-amino propionate, and the partial alkali metal salts of N-laurylbeta-iminopropionate, said additional surface active agent being present in an amount to supplement said one primary agent with the combined amount of surface active agents being not more than 45.0 grams per liter, at least one surface active agent being ionic.

2. The bath of claim 1 wherein said primary agent of said surface active component is a mixture of at least two members of said group.

3. The bath of claim 2 containing the following additional components: 0.04 to 1.5 gram per liter of a brightener selected from the group consisting of aryl alkyl aldehydes, alkyl aldehydes having a carbon chain of at least two carbon atoms, halogenated aldehydes, and benzylidene; to 30 grams per liter of a buffering agent selected from the group consisting of boric acid, acetic acid and mixtures thereof; and to 100 grams per liter of a chelating agent selected from the group consisting of citric acid, malic acid and mixtures thereof.

4. The bath of claim 3 having the following formulation:

G./l. Ammonium chloride 100-165 Zinc chloride 6095 Surface active agent 3.0-10.0 Brightener 0.04-0.5 Buffering agent 0-30 Chelating agent 10-100 G./l. Zinc chloride 65-95 Ammonium chloride 9 0-120 Surface active agent 3.07.5 Brightener 0.04-0.5 Buffering agent 0-30.0 Chelating agent 10-100 and wherein said bath has a pH of about 6.8 to 7.5.

9. The bath in accordance with claim 3 wherein said surface active component also includes at least one secondary surface active agent, said secondary surface active agent being present in an amount to supplement the primary agent with the combined amount of primary and secondary surface active agents being not more than 45.0 grams per liter.

10. The bath in accordance with claim 1 wherein said surface active component includes at least one secondary surfaceactive agent, said secondary surface active agent being present in an amount to supplement the primary agent with the combined amount of primary and secondary surface active agents being not more than 45 .0 grams per liter.

11. The bath of claim 1 additionally including 0.04 to 1.5 grams per liter of a brightener selected from the group consisting of aryl aldehydes, alkyl aldehydes having a carbon chain of at least two carbon atoms, and benzylidene.

12. The bath of claim 1 additionally including 5 to 30 grams per liter of a bufiering agent selected from the group consisting of boric acid, acetic acid and mixtures thereof.

13. The bath of claim 1 additionally including 10 to grams per liter of a chelating agent selected from the group consisting of citric acid, malic acid and mixtures thereof.

14. The bath of claim 1 wherein said ammonium chloride and zinc chloride are present in amounts of about 200 to 250 and 30 to 50 grams per liter, respectively.

.15. The bath of claim 1 wherein said ammonium chloride and zinc chloride are present in amounts of about 45 to 65 and to grams per liter, respectively.

16. The bath of claim 1 wherein said ammonium chloride and zinc chloride are present in amounts of about 70 to 120 and 65-95 grams per liter, respectively.

17. The bath of claim 1 wherein the pH is about 6.8 to 9.0.

18. The bath of claim 1 wherein said surface active component includes a mixture of an anionic phosphate ester of a polyoxyalkyl carbinamine.

19. The bath of claim 1 wherein said primary agent of said surface active component is a mixture of an imidazoline derivative with an alkyl phenol condensate.

20. The bath of claim 1 wherein said primary agent of said surface active component contains a mixture of an alkyl phenol condensate and a sulfate polyoxyalkyl carbinamine.

21. In a method for electroplating zinc, the steps comprising:

(A) preparing an aqueous bath comprising 10 to 250 grams per liter of ammonium chloride, 20 to 220 grams per liter of zinc chloride, and up to 45.0 grams per liter of a surface active component comprising a mixture of surface active agents including at least 0.75 gram per liter of a primary agent selected from the group consisting of sulfated polyoxy carbinamines, imidazoline derivatives and condensates of an alkyl phenol having an alkyl chain of 6 to 12 carbon atoms with an alkylene oxide selected from the group consisting of ethylene oxide and propylene oxide, and mixtures thereof, said bath having a pH of 3.0 to 10.0, said mixture including one of said primary agents and at least one additional surface active agent selected from the class consisting of another one of said primary agents and secondary surface active agents selected from the group consisting of phosphoric acid esters of polyalkylene glycols and alkoxylated alkyl phenols and the alkali metal salts of such esters, polyoxyalkyl carbinamines, natural phosphatides, alkyl amido betaines, the alkali metal salts of N-talloybeta-amino propionate, and the partial alkali metal salts of N-laurylbeta-iminopropionate, said additional surface active agent being present in an amount to supplement said one primary agent with the combined amount of surface active agents being not more than 45.0 grams per liter, at least one surface active agent being ionic;

(B) maintaining said bath at a temperature of about 20 to 70 centigrade;

(C) immersing a workpiece having a metallic surface and a zinc anode in said bath;

15 (D) and applying a potential across the anode and workpiece to deposit zinc on said metallic surface, said potential providing a current density of about 1.5 to 400 amperes per square foot.

22. The method in accordance with claim 21 wherein said primary agent of said surface active component contains at least two members of said group.

23. The method in accordance with claim 22 wherein said bath contains the folowing additional components: 0.04 to 1.5 grams per liter of a brightener selected from the group consisting of aryl aldehydes, alkyl aldehydes having a carbon chain of at least two carbon atoms, halogenated aldehydes and benzylidene; to '30 grams per liter of a buffering agent selected from the group consaid bath having a pH of about 6.8 to 9.0 and wherein said brightener is an aldehyde.

25. The method in accordance with claim 24 wherein said brightener is an aryl aldehyde and wherein said chelating agent is citric acid.

26. The method in accordance with claim 23 wherein said chelating agent is citric acid.

27. The method in accordance with claim 26 wherein said primary agent of said surface active component contains a mixture of an alkyl phenol condensate and a sulfated polyoxyalkyl carbinamine.

28. The method in accordance with claim 23 wherein said bath has the following formulation:

G./l. Zinc chloride 65-95 Ammonium chloride 9 0-120 Surface active agent 3.0-7.5

Brightener 0.04-0.5 Buffering agent 0-30.0 Chelating agent -100 and wherein said bath has a pH of about 6 .8 to 7.5.

29. The method in accordance with claim 23 wherein said surface active component also includes at least one secondary surface active agent, said secondary surface active agent being present in an amount to supplement the primary agent with the combined amount of primary and secondary surface active agents being not more than 45.0 grams per liter.

30. The method in accordance with claim 21 wherein said surface active component also includes at least one secondary surface active agent, said secondary surface active agent being present in an amount to supplement the primary agent with the combined amount of primary and secondary surface active agents being not more than 45.0 grams per liter.

31. The method in accordance with claim 21 wherein said bath additionally includes 0.04 to 1.5 grams per liter of a brightener selected from the group consisting of aryl aldehydes, alkyl aldehydes having a carbon chain of at least two carbon atoms, benzylidene, and halogenated aldehydes.

32. The method in accordance with claim 21 wherein said surface active component includes a mixture of an anionic phosphate ester and an polyoxyalkyl carbinamine.

33. An aqueous bath for producing a ductile, adherent zinc electroplated deposit comprising 10 to 250 grams per liter of ammonium chloride, 20 to 220 grams per liter of zinc chloride, and up to 45.0 grams per liter of a surface active component comprising a mixture of surface active agents including at least 0.7 gram per liter of a sulfated polyoxyalkyl carbinamine, said bath having a pH of 3.0-100.

References Cited UNITED STATES PATENTS 3,079,348 2/1963 Boettner et al. 252-355 3,079,416 2/1963 Dupr et al. 260-458 3,310,496 3/1967 Mansfield et al. 252-137 3,005,759 10/1961 Safranek et al. 204- R FOREIGN PATENTS 128,420 12/1945 Australia 20455 1,269,855 6/1968 Germany 204-55 GERALD L. KAPLAN, Primary Examiner 

